<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>CSS 响应式登陆表单</title>
</head>
<body>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
<h2>响应式登陆表单</h2>
<p>垂直浏览器窗口大小查看效果， 在屏幕宽度尺寸小于 650px 时，设置两列的布局上下堆叠显示。</p>

<div class="container">
    <form action="/action_page.php">
        <div class="row">
            <h2 style="text-align:center">登陆表单</h2>
            <div class="vl">
                <span class="vl-innertext">or</span>
            </div>

            <div class="col">
                <a href="#" class="fb btn">
                    <i class="fa fa-facebook fa-fw"></i> Login with Facebook
                </a>
                <a href="#" class="twitter btn">
                    <i class="fa fa-twitter fa-fw"></i> Login with Twitter
                </a>
                <a href="#" class="google btn"><i class="fa fa-google fa-fw">
                </i> Login with Google+
                </a>
            </div>

            <div class="col">
                <div class="hide-md-lg">
                    <p>Or sign in manually:</p>
                </div>

                <input type="text" name="username" placeholder="Username" required>
                <input type="password" name="password" placeholder="Password" required>
                <input type="submit" value="Login">
            </div>

        </div>
    </form>
</div>

<div class="bottom-container">
    <div class="row">
        <div class="col">
            <a href="#" style="color:white" class="btn">Sign up</a>
        </div>
        <div class="col">
            <a href="#" style="color:white" class="btn">Forgot password?</a>
        </div>
    </div>
</div>
</body>
<style>
    *{
        box-sizing: border-box;
    }
    .container{
        background-color: lightgray;
        border-radius: 5px;
        position: relative;
        padding: 20px;
    }
    .col{
        float: left;
        width: 50%;
        margin: auto;
        padding: 0 50px;
        margin-top: 6px;
    }
    .row:after {
        content: "";
        display: table;
        clear: both;
    }

    .bottom-container {
        background-color: gray;
        text-align: center;
    }
    input,.btn{
        width: 100%;
        padding: 12px;
        border: none;
        border-radius: 4px;
        margin: 5px 0;
        opacity: 0.85;
        display: inline-block;
        font-size: 17px;
        line-height: 20px;
        text-decoration: none; /* 移除锚文本链接下划线 */
    }
    .hide-md-lg{
        display: none;
    }
    .vl {
        position: absolute;
        left: 50%;
        transform: translate(-50%);
        border: 2px solid #ddd;
        height: 175px;
    }
    .vl-innertext {
        position: absolute;
        top: 50%;
        transform: translate(-50%, -50%);
        background-color: #f1f1f1;
        border: 1px solid #ccc;
        border-radius: 50%;
        padding: 8px 10px;
    }
    @media  screen and (max-width: 650px) {
        .col{
            width: 100%;
            margin-top: 0;
        }
        .vl{
            display: none;
        }

        .hide-md-lg{
            display: block;
            text-align: center;
        }

    }



</style>
</html>
